Some recent trends regarding Lake Baikal phytoplankton and zooplankton

Plankton sampling data from the period of 1951–2010 for Lake Baikal were used in this study. Data have been collected at least monthly, generally every 7–10 days, in depth profiles from the surface to 250 m at a single offshore sampling site in the southern basin, where the water depth is approximately 800 m. Measurements of abiotic variables and phytoplankton sampling were made at discrete water depths. The data for the top 50 m of the lake were averaged for temperature and biological characteristics, noting this is the water layer in the lake exhibiting most of the lake's photosynthetic production, as well as containing the most plankton organisms. Zooplankton samples were collected with a closing plankton net and enumerated at the species level and also identified by age class. Under-ice phytoplankton demonstrated the presence of some succession in spring phytoplankton, including a decreased proportion of endemic algal species. The open-water complex of the alga species demonstrated that some non-endemic species exhibited positive trends. The zooplankton analyses demonstrated a noticeable increasing trend for total zooplankton, the main zooplankton components being Epischura baicalensis, as well as increased Cladoceran numbers. These trends can be hypothetically explained by the following: (i) global climate change (although Lake Baikal also exhibits long-term temperature oscillations); (ii) regional warming (due to construction of reservoir systems during the 1950s–1970s period); (iii) local chemical pollution attributable to increased industrial and agricultural activity in the lake's watershed and airshed basins; and/or (iv) the natural oscillating behaviour of the lake's plankton components.